Add sandbox_c cmake project + ccache workflow for pool testing

sandbox_c/src/parse.c

@@ -0,0 +1,34 @@
+#include "temperature.h"
+#include <stdlib.h>
+#include <string.h>
+
+/* Deliberately tiny parser: finds "celsius":<num> and an optional
+   "sensor":"..." so the test can assert on both fields. */
+int parse_reading(const char *json, Reading *out) {
+    if (!json || !out) return 1;
+    const char *c = strstr(json, "\"celsius\"");
+    const char *s = strstr(json, "\"sensor\"");
+    if (!c) return 2;
+    c = strchr(c, ':');
+    if (!c) return 3;
+    char *end = NULL;
+    out->celsius = strtod(c + 1, &end);
+    if (end == c + 1) return 4;
+    out->sensor[0] = '\0';
+    if (s) {
+        s = strchr(s, ':');
+        if (s) {
+            const char *open = strchr(s, '"');
+            if (open) {
+                const char *close = strchr(open + 1, '"');
+                if (close) {
+                    size_t n = (size_t)(close - open - 1);
+                    if (n >= sizeof out->sensor) n = sizeof out->sensor - 1;
+                    memcpy(out->sensor, open + 1, n);
+                    out->sensor[n] = '\0';
+                }
+            }
+        }
+    }
+    return 0;
+}